Blow molding device for producing thermoplastic containers

ABSTRACT

The invention concerns a device for producing thermoplastic containers, in particular bottles, by the blow-molding or stretch blow-molding of a preheated preform. The device comprises at least one mould consisting of two half-molds ( 2 ) each supported by a mould carrier, the two mould carriers being movable relative to each other. Each half-mould ( 2 ) comprises a shell holder ( 9 ), supported by the respective mould carrier, and a shell ( 7 ) which is equipped with a half-impression ( 8 ) of the container to be obtained and can be rendered integral in a detachable manner with its shell holder ( 9 ) by rapid-fastening means ( 19-23 ). The shell ( 7 ) and the shell holder ( 9 ) are of complementary shapes such that they contact each other at least partially for heat conduction purposes whilst the pipes and connections for circulating and/or heating fluids are provided in the shell holder alone.

Notice: More than one reissue application has been filed for the reissueof U.S. Pat. No. 5,968,560. The reissue applications are applicationNos. 09/553,413 (the present application) and 09/902,475. ApplicationNo. 09/902,475 is a continuation of application No. 09/553,413.

The present invention relates to improvements made to devices making itpossible to manufacture containers, in particular bottles, made of athermoplastic by blow molding or stretch-blow molding of a preheatedpreform, the said device including at least one mold consisting of twohalf-molds respectively supported by two mold carriers which can moveone with respect to the other.

It is common practice for the half-molds to be removably fixed to therespective mold carriers so that the said half-molds can be replaced orchanged should they become damaged and/or worn and, above all, shouldcontainers of different shapes and/or sizes be manufactured, without itbeing necessary to replace the entire molding device.

However, such an arrangement is still far from being to the completesatisfaction of users. This is because each half-mold is heavy (forexample about 25 to 30 kg for a steel mold): the fixing means must beable to support this weight and comprise many nut-and-bolt and/or screwconnections; furthermore, each half-mold must be handled by severalpeople and/or by means of a hoist, thereby requiring a suitableinstallation above the manufacturing device. Each half-mold is equippedwith means for the circulation of one or more fluids for the coolingand/or heating of the walls of the impression: replacing each half-moldis accompanied by disconnecting, followed by reconnecting, of thecorresponding fluid connections, all operations requiring time.

It is also necessary to add an economic consideration regarding theactual construction of each half-mold. The impression serving forpressure molding the final container must have a perfectly polishedsurface finish, to which, furthermore, the hot thermoplastic must notadhere: it is therefore necessary for the impression to be made of asuitable metallic material (for example stainless steel) which,moreover, may differ depending on the thermoplastic employed. Given themonobloc structure of the half-mold, it is therefore the totality ofeach half-mold which must be made of this suitable metallic material,this being a special and therefore expensive material, while the rearpart of the half-molds merely fulfills a mechanical strength function,giving the mold rigidity and non-deformability, for which rear part amore ordinary, and therefore less expensive, material could be perfectlysuitable.

The object of the invention is therefore essentially to remedy, as faras is possible, the drawbacks of the currently known manufacturingdevices and to provide an improved device which allows quick and simplechanging of the molding impressions in order to make it easier to adaptthe device to the manufacture of various containers, and the improvedstructure of which device is, at the end of the day, less expensive thanthat of the current devices while still maintaining the same strengthand non-deformability properties.

To these ends, a device for manufacturing thermoplastic containers, asmentioned in the preamble, is essentially characterized, being designedin accordance with the invention, in that each half-mold comprises ashell holder supported by the respective mold carrier and a shell whichis provided with a half-impression of the container to be obtained andwhich can be removably fastened to its shell holder by quick-fixingmeans, the shell and the shell holder being of complementary shapes inorder to be in at least partial mutual contact, with thermal conduction,while the pipes and connections for the circulation of cooling and/orheating fluids, and optionally the members for guiding the half-molds inorder to close the mold, as well as the pressure-compensating means formaintaining the sealed closure of the mold during blow molding, areprovided exclusively in the shell holder.

By virtue of this arrangement, the part of the half-mold correspondingto the impression, which may be economically made of a suitable andrelatively expensive material, and the rear part of the half-mold, whichprovides rigidity and mechanical strength and which may be made of amore ordinary and less expensive material (for example a standardaluminum alloy), are separated from each other. In addition, being lessheavy, this rear part has less inertia, thereby contributing tofacilitating the rotational movements of the half-molds. In addition,and above all, changing the impression in order to manufacturecontainers of various shapes merely requires changing the shell, whichis of a much lower weight (for example about 10 kg) compared to thecomplete half-mold and which can therefore be handled manually: thehandling installation (which, however, remains necessary in order tohandle other components, and in particular the shell holders, of thedevice) may, however, be simplified and, above all, the procedure forreplacing the shells is speeded up. This procedure is, furthermore, madeeven more rapid as there are no longer the fluid fittings to bedisconnected, and then reconnected, these remaining permanentlyconnected to the shell holders.

It is also possible to standardize the shell holders which are, from theoutset, equipped with a number of fluid pipes from among which thoseuseful for a given manufacture with a given impression may be selected.Thus, it is possible to create independent circuits making it possibleto produce, in each shell holder and therefore in the shell, regionswith differentiated temperature settings. Here again, this results inthe possibility of reducing the manufacturing cost of the shell holders,which accompanies their standardized production in larger number.

Preferably, the mutually contacting mating faces of the shell and of theshell holder are approximately semicylindrical surfaces of revolutionwith an axis approximately parallel to the axis of the impression of thecontainer to be manufactured; it is thus easier to producemutually-contacting mating faces which ensure heat transfer as close aspossible to that of a monobloc structure, something which mayfurthermore be obtained by providing for the shell and the shell holderto be in total thermal-conduction contact. However, it should be notedhere that the arrangement according to the invention also provides thepossibility of ensuring, when this proves to be desirable, that theshell and the shell holder are in partial thermal-conduction contact byleaving regions of limited thermal conduction, which also constitutesanother means of creating, in the wall of the impression, regions withdifferentiated temperature settings.

It is desirable, in order to allow quick, and therefore easy, assemblyof the shell on the shell holder, while still having precise relativepositioning of the shells one with respect to the other, for themutually-contacting mating faces, with thermal conduction, of the shelland of the shell holder to be provided with axial mutual-positioningmeans; preferably, the said axial mutual-positioning means comprise asystem of one or more mating ribs and grooves extendingcircumferentially, which arrangement, in combination with theaforementioned semicylindrical configuration of the said mating faces ofthe Shell and of the shell holder, allows very simple assembly, withvery precise positioning of the shell, using simplified fixing means.

Thus, advantageously, the means for quickly fixing the shell to theshell holder are provided on their respective parting faces. In the caseof semicylindrical mating faces, the said fixing means are located onthe respective edges of the shell and of the half-shell, these beingparallel to the axis of the impression; it is then desirable for thequick-fixing means to comprise, on one side, at least one stop forpositioning the parting face of the shell with respect to the partingface of the shell holder and, on the other side, quick-screwing means onthe parting face of the shell holder with a clamping surface projectingfrom the parting face of the shell, by virtue of which the shell is putinto place on and locked onto the shell holder by curvilinear sliding ofthe shell, guided by the rib(s)/groove(s) system, in the cradle formedby the shell holder. In particular, if the mold carriers arerotationally pivoted with respect to each other, in order to form a“jackknife”-type mold, provision is made, in order to simplifyconnection and disconnection, for the abovementioned stop to be locatedon the pivot side of the mold carriers and the quick-screwing means tobe located on the opposite side.

In order to be more specific, it may be pointed out that, in a typicalmolding device designed in accordance with the invention, the time toreplace a pair of shells is about 8 minutes while the time to replace apair of half-shells in a prior device is about 20 minutes, usingappropriate handling equipment.

The invention will be more clearly understood on reading the detaileddescription which follows of a preferred embodiment given solely by wayof illustrative example. In this description, reference is made to theappended drawings in which:

FIG. 1 is a diagrammatic view from above of part of a molding devicedesigned in accordance with the invention;

FIG. 2 is a front view of a two-piece half-mold of the device in FIG. 1;and

FIG. 3 is a view from below of a half-mold in FIG. 2.

FIG. 4 is a view from left, partially cutaway, of the device of FIG. 1.

Referring first of all to FIG. 1, this shows part of a device formanufacturing containers, in particular bottles, made of a thermoplasticsuch as polyethylene terephthalate PET, polyethylene apththalate PEN oranother material, as well as alloys or blends thereof, by blow moldingor stretch-blow molding a preheated preform.

This device includes at least one mold 1 consisting of two half-molds 2respectively supported by two mold carriers 3 which can move one withrespect to the other. In the example shown, the two mold carriers 3 aremade in the form of two enveloping structures pivotally mounted on acommon rotation axis 4 in such a way that the two half-molds can moveapart by pivoting (a socalled “jackknife” structure). The mold carriersmay be driven, in order to open and close the mold, in a conventionalmanner using a system of traction arms pivoted at 5 to the respectivemold carriers a certain distance from the axis 4 of the latter.

Locking means, denoted in their entirety by 6, lock the two half-moldsin the closed, molding position.

In accordance with the invention, each half-mold is made in the form oftwo subassemblies, namely a shell 7 provided with a half-impression 8 ofthe container to be manufactured and a shell holder 9 which supports theshell 7 and which is itself fastened to the corresponding mold carrier2.

Each shell holder 9 may be considered as corresponding externally, inshape and size, to the mold carrier of the previous structures and itmay therefore be fastened to the respective mold carrier 3 in the samemanner, for example by a nut-and-bolt connection 10, it being possiblefor the number and disposition of the holes and internal threads to beidentical to those of the previous arrangements.

As may be seen in FIG. 3, each shell holder is provided with internalpipes 11 and with fittings 12 which are necessary for the circulation ofat least one fluid for cooling or heating the wall of the impression.Any number of these pipes and fittings may be provided and they may, forexample, be independent of each other so as subsequently to allow themcomplete freedom, by externally connecting them appropriately, toconstitute circuits of various and/or independent configurationsdepending on the type of containers to be produced and the type ofmaterial employed. Thus, it is possible to standardize to some extentthe manufacture of the shell holders 9 and to reduce the manufacturingcost thereof.

Because of the fact that the impression 8 is physically separated fromthe shell holder 9, it is possible to make the latter from a lessspecial material, for example an ordinary aluminum alloy, even when theshell is made of steel, thereby making it possible, here too, to reduceits cost; in addition, the shell holder 9 thus produced is lighter thana steel shell holder, which desirably decreases its inertia and has afavorable effect on the dynamic operation of the mold.

Each shell 7 has a half-impression 8 of the final container, hollowedout in its parting face 13. The external face 14 of each shell 7 has thegeneral shape of a semicylinder of revolution, the axis of which isapproximately parallel to the axis of the impression 8 of the container;in practice, the impression is coaxial with the semicylinder. The shell7 rests in a cradle 15 of complementary shape cut out in the shellholder 9. The shapes of the shell and shell holder are perfectly matchedand they are thus in as close a contact as possible. Provision may thusbe made for the mating faces 14 and 15 of the shell 7 and of the shellholder 9 to be in complete thermal-conduction contact so that heattransfer from one to the other is as good as possible and approaches asfar as possible that of a monobloc half-mold.

However, it is also conceivable for the said mating faces 14 and 15 tobe only partially in thermal-conduction contact, with provision ofregions of limited thermal conduction; it is thus possible to producedifferentiated temperature settings in the wall of the impression. Inorder for the impression 8 to have the required polished finish and forthe hot thermoplastic not to adhere to its surface, the shells are madefrom a suitable material, for example stainless steel. In order for theshapes of the mating parts of the shell holder 9 and the shell 7 toremain perfectly matched, it is necessary to choose materials exhibitingthermal expansion coefficients which are substantially identical.

In the example shown in FIG. 2, the container to be produced has abottom of complex shape (petaloid bottom) and the requirements fordemolding the container after it has been formed result in the provisionof a separate mold bottom 25, distinct from the half-molds 2, whichincludes the impression of the bottom of the container. It will be notedhere that FIG. 3 is a view from below of the half-mold in FIG. 2, themold bottom 25 not being shown.

The axial mutual positioning of the shell holder 9 and of the shell 7 isachieved by a rib(s)/groove(s) set of mating elements which fittogether, one in the other. As shown in FIG. 2, the shell 7 is providedwith two grooves 17, hollowed out circumferentially in its external face14 axially separated from each other; likewise, the cradle-shaped face15 of the shell holder 9 has two ribs 16 which fit together without anyclearance in the two respective grooves 17. Once the shell 7 has beenplaced in the shell holder 9, it can no longer move axially with respectto the latter but can only slide rotationally about its axis on thecradle 15.

In order fully to lock the shell onto the shell holder, quick-fixingmeans are provided in the parting face 13 of the shell and in theparting face 18 of the shell holder. For this purpose, respectivehousings 19 and 20, hollowed out in the facing edges of theafore-mentioned parting faces 13 and 18, respectively, are provided. Thebottoms of the housings 19 of the shell 7 constitute flat bearingsurfaces on which may bear members for locking the shell holder 9. Theselocking members may be formed in many ways known to those skilled in theart. In the example shown in FIG. 2, these are projecting lugs 21drilled with an elongate hole 22 and retained by a screw 23 fixed to thebottom of the corresponding housing 20 of the parting face 18 of theshell holder 9; this arrangement has the advantage that the shell isreleased as soon as the lugs 21 are unlocked and pushed back toward theoutside, without it being necessary to remove the screws 23 completely.Notwithstanding this, the shell could also be locked onto the shellholder by using wide-head screws overlapping the flats of the housings19, or else by using quick-face eccentric-head screws, etc.

It will be noted that in practice the two locking members 21 located onthe side adjacent to the axis of rotation 4, in the case of a jackknifemold, do not have to be actuated and may thus constitute simple stops(with the possibility of adjusting the position of these stops) underwhich the flats of the respective housings 19 are brought when the shellis inserted into the shell holder, by causing the shell to sliderotationally in the latter. Moreover, given the position of these twolocking members 21 located in the bottom of the open mold, their accessis difficult and their removal would unnecessarily lengthen the processof replacing the shell 7.

As for the rest, each shell holder 9 is designed in the same way as aprevious half-mold, which includes the elements necessary for correctoperation of the molding device, and in particular the means 10 forfixing it to the corresponding mold carrier 3, the guiding fingers 24(and the respective housings in the other shell holder) for closing themold, the rear face provided with a chamber 26 and with an O-ring seal27 for compensation as shown in FIG. 4. It is therefore possible, in apreexisting installation, to replace the conventional monoblochalf-molds with two-element half-molds according to the invention.

Needless to say, and as results already from the foregoing, theinvention is in no way limited to those of its methods of applicationand of its embodiments which have been more particularly envisaged; onthe contrary, it embraces all variants thereof.

1. Device for manufacturing containers, made of a thermoplastic by blowmolding or stretch-blow molding of a preheated preform, the said deviceincluding at least one mold (1) consisting of two half-molds (2)respectively supported by two mold carriers (3) which are made in theform of enveloping structures and which can move one with respect to theother, characterized in that each half-mold (2) comprises a shell holder(9) supported by the respective mold carrier (3) and a shell (7) whichis provided with a half-impression (8) of the container to be obtainedand which can be removably fastened to its shell holder (9) byquick-fixing means (19-23), the shell (7) and the shell holder (9) beingin complementary shapes in order to be in at least partial mutualthermal-conduction contact while the pipes and connections for thecirculation of cooling and/or heating fluids (11, 12) are providedexclusively in the shell holder.
 2. Device according to claim 1,characterized in that the mating faces (14, 15) of the shell (7) and ofthe shell holder (9) are in total thermal-conduction contact.
 3. Deviceaccording to claim 1, characterized in that the mating faces (14, 15) ofthe shell (7) and of the shell holder (9) are in partialthermal-conduction contact by leaving regions of limited thermalconduction.
 4. Device according to claim 1, characterized in that themutually contacting mating faces (14, 15) of the shell (7) and of theshell holder (9) are approximately semicylindrical surfaces ofrevolution with an axis approximately parallel to the axis of theimpression (8) of the container to be manufactured.
 5. Device accordingto claim 1, characterized in that the mutually contacting mating faces(14, 15) of the shell and of the shell holder are provided with axialmutual-positioning means (16, 17).
 6. Device according to claim 5,characterized in that the axial mutual-positioning means comprise asystem of one or more mating ribs (16) and grooves (17) extendingcircumferentially.
 7. Device according to claim 1, characterized in thatthe means (19-23) for quickly fixing the shell (7) to the shell holder(9) are provided on their respective parting faces (13, 18).
 8. Deviceaccording to Claim 4, characterized in that the means (19-23) forquickly fixing the shell and the shell holder are located on theirrespective edges parallel to the axis of the impression.
 9. Deviceaccording to claim 8, characterized in that the quick-fixing means(19-23) comprise, on one side, at least one stop for positioning theparting face of the shell with respect to the parting face of the shellholder and, on the other side, quick-screwing means (23) on the partingface (18) of the shell holder (9) with a clamping surface (21)projecting from the parting face (19) of the shell.
 10. Device accordingto claim 9, in which the mold carriers are rotationally pivoted withrespect to each other whereby at least one stop is located on the pivot(4) side of the mold carriers (3) and the quick-screwing means arelocated on the opposite side.
 11. Device according to claim 1,characterized in that the shell holder (9) is also provided with members(24) for guiding the half-molds in order to close the mold.
 12. Deviceaccording to claim 1, characterized in that at least one of the shellholders is equipped with pressure-compensating means suitable formaintaining the sealed closure of the mold during blow molding. 13.Device according to claim 1, characterized in that the shell holders (9)are equipped with a number of fluid pipes, by virtue of which it ispossible to create suitable circuits for a given manufacture with agiven impression.
 14. Device according to claim 1, wherein saidcontainers are bottles.
 15. A mold assembly for use in manufacturingmolded thermoplastic containers comprising: two mold shells eachcontaining a half-impression of a substantial portion of the containerto be molded; two mold shell holders each defining a cavity forreceiving each said respective mold shell such that each said respectivemold shell is in at least partial mutual thermal-conduction contact withits respective shell holder, said shell holders being shaped to besupported by two mold carriers made in the form of enveloping structuresmovable one with respect to the other; and at least one quick-fixinglocking member by which at least one of said mold shells is removablysecured to a respective one of said mold shell holders, said onequick-fixing locking member including a selectively retractable lockingmember portion.
 16. The mold assembly of claim 15, further comprising atleast one axial positioning assembly by which said mold shells are fixedin an axial direction with respect to said mold shell holders.
 17. Themold assembly of claim 16, wherein said axial positioning assemblycomprises at least one meshing coupling member disposed on at least oneof said mold shells and mold shell holders, and at least onecomplementary meshing coupling member disposed on at least one of saidmold shells and mold shell holders.
 18. The mold assembly of claim 15,wherein said mold shell holders further comprise a number of internalfluid pipes and connections for the circulation of cooling and/orheating fluids.
 19. The mold assembly of claim 15, wherein at least oneof said mold shells and/or mold shell holders define at least one cavityat the interface between said mold shells and mold shell holders intowhich pressurized fluid suitable for maintaining the sealed closures ofthe mold assembly may be interposed during the molding process.
 20. Themold assembly of claim 17, wherein said meshing coupling members furthercomprise a system of one or more mating ribs and grooves in said moldshells and mold shell holders.
 21. The mold assembly of claim 15,wherein said quick-fixing locking member comprises, on one side, atleast one stop for positioning the parting face of said mold shell withrespect to said mold shell holder and, on the other side, at least onequick-acting screw on the parting face of said mold shell holder with atleast one clamping surface projecting from the parting face of said moldshell.
 22. The mold assembly as claimed in claim 15, wherein saidquick-fixing locking member is configured to include a portion whichremains engaged with said mold shell holder when said quick fixinglocking member is moved out of said locking position.
 23. A moldassembly for use in manufacturing molded thermoplastic containerscomprising: two mold shells each containing a half-impression of asubstantial portion of the container to be molded; two mold shellholders each defining a cavity for receiving each said respective moldshell such that each said respective mold shell is in at least partialmutual thermal-conduction contact with its respective shell holder, saidshell holders being shaped to be supported by two mold carriers made inthe form of enveloping structures movable one with respect to the other;and at least one quick-fixing locking member by which at least one ofsaid mold shells is removably secured to a respective one of said moldshell holders, said quick-fixing locking member itself including aretractable locking member portion which can be selectively extended andretracted such that when extended, said retractable locking memberportion provides at least partial securement of said one of said moldshells relative to said corresponding mold shell holder, and whenretracted, said retractable locking member portion does not providesecurement of said one said mold shells relative to said correspondingmold shell holder.
 24. A mold assembly for use in manufacturing moldedthermoplastic containers comprising: two mold shells each containing ahalf-impression of a substantial portion of the container to be molded;two mold shell holders each defining a cavity for receiving each saidrespective mold shell such that each said respective mold shell is in atleast partial mutual thermal-conduction contact with its respectiveshell holder, said shell holders being shaped to be supported by twomold carriers made in the form of enveloping structures movable one withrespect to the other; and at least one quick-fixing locking member bywhich at least one of said mold shells is removably secured to arespective one of said mold shell holders, said one quick-fixing lockingmember including a selectively movable locking member portion which canbe selectively moved into and out of a locking position which at leastpartially locks said one of said mold shells to said respective moldshell holder, and said quick-fixing locking member is configured toinclude a portion which remains engaged with said mold shell holder whensaid quick fixing locking member is moved out of said locking position.25. The mold assembly as claimed in claim 24, wherein said quick-fixinglocking member comprises the following portions: a fastener portion; andsaid selectively movable locking member portion, said fastener portionand said selectively movable locking member portion being separate butconfigured to interact such that said fastener portion remains engagedwith said mold shell holder when said locking member portion is movedout of said locking position.
 26. The mold assembly as claimed in claim25, wherein said fastener portion is threadably engaged with said moldshell holder through a threaded connection that can be partiallyloosened without disengagement to allow said locking member portion tobe moved out of said locking position.
 27. A mold assembly for use inmanufacturing molded thermoplastic containers comprising: two moldshells each containing a half-impression of a substantial portion of thecontainer to be molded; two mold shell holders each defining a cavityfor receiving each said respective mold shell such that each saidrespective mold shell is in at least partial mutual thermal-conductioncontact with its respective shell holder, said shell holders beingshaped to be supported by two mold carriers made in the form ofenveloping structures movable one with respect to the other; and atleast one quick-fixing slidable lock by which at least one of said moldshells is removably secured to a respective one of said mold shellholders, said slidable lock being slidable into and out of a lockingposition which at least partially locks said one of said mold shellsrelative to said respective mold shell holder.
 28. The mold assembly asclaimed in claim 27, wherein said quick-fixing slidable lock isconfigured to include a portion which remains engaged with said moldshell holder when another portion of said quick fixing locking member ismoved out of said locking position.